1. Field of the Invention
The present invention relates to an apparatus for image transformation of an input image to an output image and more particularly to an apparatus for image transformation which reduces aliasing occurring at the edge portion of the output picture when an input image is transformed.
2. Description of the Prior Art
Apparatus for image transformation which, when applied to television broadcasting and production of an animation, subject an input image to such transformations as rotation, magnification, reduction, and movement, or spread an input image over a curved surface in a three-dimensional coordinate system, to thereby generate an output image are well known, as for example, shown in the gazette of Japanese Laid-open Patent Publication No. 61-230477.
In an apparatus for image transformation of a type which, when generating an output image by transforming an input image, produces the image data of each pixel of the output image by performing an interpolating calculation on four sets of picture data of the input image, the output image obtained by such a transformation of an input image becomes jagged exhibiting a stair-step appearance at its edge portion, which is the so-called aliasing effect. There has so far been known an art to reduce such an aliasing by applying a two-dimensional digital filter to an output image so that the data at the edge portion of the output image are averaged. However, if image data are averaged by means of such a two-dimensional digital filter, the edge portion of the output image becomes a blurred line and the resolution there becomes deteriorated.